Tax collectors were also often called publicans. They worked for the Roman government and were generally despised by the Jewish people. Tax collectors or publicans could not testify in a court of law, and they could not tithe to the local temple.

The Jews considered a tax collector's money to be unclean. Therefore, a Jewish man would never ask a tax collector for change. If a Jewish man did not have the exact amount of money owed, he would borrow it from a friend.

The biggest struggle between Jews and Romans was over taxes. Jews had been paying taxes to Rome since 63 B.C. But when Rome added Judea to their province, the people of Palestine had to pay even more taxes. Obviously, this did not make the Jews very happy. Adding to the Jews' anger, tax collectors were often encouraged to overcharge or to be dishonest in their collection of the taxes.
(The New Unger's Bible Dictionary, s.v. "Matthew", "Tax-gatherer" Chicago: Moody Press, 1988. Illustrated Encyclopedia of Bible Facts, s.v. "The Romans" Nashville: Thomas Nelson Publishers,1995.)